Carbon dioxide exchange between an undisturbed old-growth temperate forest and the atmosphere

• Published in: Ecology (Durham) 1994-01, Vol.75 (1), p.134-150
• Main Authors: Hollinger, D. Y., Kelliher, F. M., Byers, J. N., Hunt, J. E., McSeveny, T. M., Weir, P. L.
• Format: Article
• Language: English
• Subjects: AIR TEMPERATURE; Animal and plant ecology; Animal, plant and microbial ecology; Atmosphere; Biological and medical sciences; BREATHING; CARBON DIOXIDE; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; ECHANGE GAZEUX; ECOSISTEMA; Ecosystem models; ECOSYSTEME; ECOSYSTEMS; ENVIRONMENTAL FACTORS; FACTEUR DU MILIEU; FACTORES AMBIENTALES; Forest canopy; Forest ecology; Forest ecosystems; Forests; Fundamental and applied biological sciences. Psychology; GAS EXCHANGE; INTERCAMBIO DE GASES; LIGHT; LIGHT RELATIONS; LUMIERE; LUZ; NEW ZEALAND; NOTHOFAGUS; NOUVELLE ZELANDE; NUEVA ZELANDIA; Old growth forests; RESPIRACION; RESPIRATION; Summer; Synecology; TEMPERATURA DEL AIRE; TEMPERATURE DE L'AIR; Terrestrial ecosystems; UPTAKE; Wind velocity
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1939390

We used the eddy-correlation technique to investigate the exchange of CO"2 between an undisturbed old-growth forest and the atmosphere at a remote Southern Hemisphere site on 15 d between 1989 and 1990. Our goal was to determine how environmental factors regulate ecosystem CO"2 exchange, and to test whether present knowledge of leaf-level processes was sufficient to understand ecosystem-level exchange. On clear summer days the maximum rate of net ecosystem CO"2 uptake exceeded 15 @mmol@?m^-^2@?s^-^1, about an order of magnitude greater than the maximum values observed on sunny days in the winter. Mean nighttime respiration rates varied between @?-2 and -7 @mmol@?m^-^2@?s^-^1. Nighttime CO"2 efflux rate roughly doubled with a 10@?C increase in temperature. Daytime variation in net ecosystem CO"2 exchange rate was primarily associated with changes in total photosynthetically active photon flux density (PPFD). Air temperature, saturation deficit, and the diffuse PPFD were of lesser, but still significant, influence. These results are in broad agreement with expectations based on the biochemistry of leaf gas exchange and penetration of radiation through a canopy. However, at night, the short-term exchange of CO"2 between the forest and the atmosphere appeared to be regulated principally by atmospheric transport processes. There was a positive linear relationship between nocturnal CO"2 exchange rate and downward sensible heat flux density. This new result has implications for the development of models for diurnal ecosystem CO"2 exchange. The daytime light-use efficiency of the ecosystem (CO"2 uptake/incident PPFD) was between 1.6 and 7.1 mmol/mol on clear days in the summer but decreased to 0.8 mmol/mol after frosts on clear winter days. Ecosystem CO"2 uptake was enhanced by diffuse PPFD, a result of potentially global significance given recent increases in Northern Hemisphere haze.